The present disclosure relates generally to heat exchanger systems, such as heat exchanger systems for aircraft.
Heat exchangers are devices that transfer heat from one fluid to another and may be used in refrigeration, air conditioning, space heating, electricity generation and chemical processing. For example, heat exchangers may be used in the aerospace and automobile industries.
In aircraft applications, Federal Aviation Regulations (FAR) from the Federal Aviation Administration (FAA) set standards for different aircraft operating conditions. For example, FAR airworthiness standards exist for transport category airplanes relating to fresh air requirements. In order to meet these different FAR standards, modifications or changes to different systems or components may be needed. As one example, in order to meet passenger fresh air requirements with existing aircraft cooling packs that include heat exchangers, the engine bleed system needs to deliver higher pressure bleed air than under normal operating pressure conditions. During the cruise phase of a flight, the thrust required by the aircraft slowly decreases as the weight of the vehicle decreases. Bleed air pressure also decreases with the decreasing engine thrust. As a result, bleed air temperature also decreases, which results in the air cooling a heat exchanger to shut off.
At some point during the cruise, the engine bleed system switches the bleed port to a higher stage of the engine high pressure compressor to meet the cooling pack requirement. When the bleed system switches to a higher stage of air cooling, the heat exchanger is increased to a maximum operating level, with the energy extracted from the engine greatly increased, thus, resulting in a negative impact on the specific fuel consumption (SFC) of the engine. Accordingly, fuel burn during flight is increased.
Known systems to meet the cooling pack pressure requirements on the low stage bleed during cruise include engine re-designs. However, this re-design to utilize lower air pressure adversely affects other flight phases and is costly both in design and certification.